Summerhall @ Roundabout, EdinburghThis vigorous but sketchy play asks what you do if you discover you're not who you thought you were

What happens to a society when reality is revealed as a complete lie? … Steven Webb in Mark Ravenhill's Show 6. Click to view full image Photograph: Murdo MacLeod for the Guardian Murdo MacLeod/Guardian

Paines Plough's nifty travelling space offers a temporary home for the latest from the Lyric Hammersmith's Secret Theatre. In traditional Secret Theatre style the show comes without a title, but in a departure from past practice its author, Mark Ravenhill, was announced in advance. It features only three of the permanent ensemble, who can be glimpsed in their full glory around the corner at Northern Stage in the confidently quirky A Series of Increasingly Impossible Acts.

There's more than a touch of Greek tragedy about a scenario in which a car crash leads a spoiled young man to discover, Oedipus-style, that he is not his parents' child. The piece, with its sphinx-like intimations, takes inspiration not only from Sophocles but also from the experiences of children who grew up in Chile. Many have discovered that their biological parents were opponents of the Pinochet dictatorship, opponents who were "disappeared". The children were given to families who supported the regime and raised them as their own.

The young, nameless man in Ravenhill's play has grown up with privilege, but neuroticism is never far away. He is in thrall to his would-be incestuous adoptive mother and, like his peers, is a regular drug user. What do you do if you discover that you are not the person you thought that you were? What happens to a society when the constructed reality is revealed as a lie? Retreat into more lies and self-deceptions – or plot revolution?

There's plenty to admire in the performances from Cara Hogan, Steven Webb and Matti Houghton, and Ravenhill's writing is typically vigorous. But South American playwrights and theatre-makers have covered this territory with greater ownership and complexity – and far more passion – and this contribution never feels like more than a sketch, or an outline for a knottier play.